1. Field of the Invention
This invention relates to a magnetic toner used in recording processes such as electrophotography, electrostatic recording, magnetic recording and so forth.
2. Related Background Art
A number of methods are conventionally known as methods for electrophotography. In general, copies or prints are obtained by forming an electrostatic latent image on an electrostatically charged image bearing member (hereinafter also “photosensitive member”) utilizing a photoconductive material and various means, subsequently developing the latent image by the use of a toner to form a toner image as a visible image, transferring the toner image to a recording medium such as paper as needed, and then fixing the toner image onto the recording medium by the action of heat and/or pressure. Apparatus for such image formation include copying machines, printers and so forth.
In recent years, these printers or copying machines have progressed from analogue machines to digital machines, and it is required to have a good reproducibility of latent images, be free of spots around line images and so forth, and have a high image quality. Also, at the same time, the main bodies of such printers or copying machines are increasingly miniaturized.
Here, taking note of, for example, printers, The use of printers is being divided into two forms. One is a large-sized printer adaptable to a network, where the printing is often performed on a large number of sheets at one time. The other is a personal printer for personal use in offices or in SOHO (small office home office). The personal printer is used in a low print percentage on account of its use form, and the printing is often performed on one or few sheets. Where printing is performed on few sheets at one time (hereinafter called “intermittent mode”), a high load is applied to the toner, as compared with the occasion of continuous printing on a large number of sheets, and the deterioration of the toner tends to be accelerated. This tendency is strong especially in an intermittent mode with a low print percentage in a high-temperature and high-humidity environment.
In particular, the personal printer is strongly desired to be miniaturized in respect of not only its main body but also its developing assembly itself. With such a trend, each of the component parts including a toner carrying member is also increasingly miniaturized. However, taking note of an image bearing member used along with a magnetic developer, the miniaturization of the toner carrying member is to reduce the diameter of the toner carrying member, and means that a magnet roller set in the toner carrying member also must be miniaturized. In this case, with a decrease in diameter of the magnet roller, the magnetic flux density inevitably decreases, tending to increase fog in a low-temperature and low-humidity environment. Moreover, it is essential for the toner to have a smaller particle diameter in order to achieve higher image quality, which is apt to increase fog.
To cope with such a problem, Japanese Patent Application Laid-open No. 2001-235898 proposes a spherical toner which makes use of a magnetic powder containing a phosphorus element. This toner has a superior resolution, and has a superior running (extensive operation) performance in a high-temperature and high-humidity environment. However, there is room for further improvement when used in the intermittent mode with a low print percentage in a high-temperature and high-humidity environment and a low-temperature and low-humidity environment.
In addition, the miniaturization of the developing assembly can be achieved not only by miniaturizing its component parts but also by reducing toner consumption. Accordingly, reduction in toner consumption is also strongly required.
In general, monochrome printers or copying machines are often used to reproduce letters or characters, where the toner consumption can be reduced by controlling what is called the toner amount laid on line (the toner amount used for developing line images). However, for example, in an attempt to form a line latent image of 200 μm in width and control the toner consumption, there has been such a problem that the line width actually obtained is fairly smaller than 200 μm, resulting in a lowering of the reproducibility of latent images.
In Japanese Patent Application Laid-Open No. H01-112253, there is the proposal that the toner consumption can be reduced by using a toner having a specific fine-powder content, true density and residual magnetization. However, such a toner tends to give a low solid-image density, and an attempt to increase the image density results in an increase in toner consumption and also in the line thickness.
That is, it has been very difficult to keep the image density high and reproduce lines faithfully to latent images while reducing the toner consumption.
Thus, in furtherance of miniaturizing the main body, toner is required to enjoy a low consumption and to provide good images in long-term use in various environments. In order to satisfy such requirements, room is still left for further improvement.